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An Overview of AHSEC now ASSEB Class 12 Biology Notes for 2025
| Name of Board | AHSEC |
| Class: | Assam Board Class 12 |
| Subject: | ASSEB/AHSEC Class 12 Biology |
| Number of Chapter: | 13 |
| Chapter Name | Biodiversity and Conservation |
| Content Type: | Text, Images and PDF Format |
| Academic Year: | 2025-26 |
| Medium: | English Medium |
| Available Solution Link: | AHSEC Class Biology Notes |
[A] FILL IN THE BLANKS (1 MARK EACH)
1. According to IUCN (2004) there are slightly more than_____ earth. million plant and animal species described from
Ans. 1.5 million
2. Species diversity_____equator to the pole. as one moves away from the
Ans. Decreases
3. The rain forest covers no more than____per cent of earth surface.
Ans. 6%
4. Exploring molecular genetic and species -level diversity for products of economic importance is called______
Ans. Bioprospecting
5. There are number of biosphere reserves in India.
Ans. 14 (Fourteen)
6. The total land area of Orang National park is_______km²
Ans. 78.81 sq km
[B] TRUE OR FALSE (1 MARK EACH)
1. Plots with higher number of species show less year to year variation in total biomass.
Ans. True.
2. Water hyacinth (Eicchornia) is a native species of India.
Ans. False.
3. The higher productivity of tropics is due to higher availability of solar energy.
Ans. True.
4. There are two biosphere reserves in Assam.
Ans. True.
5. Forest cover in Assam is about 50% of the total geographical area.
Ans. False.
6. Kaziranga is the abode of pigmy hog.
Ans. False.
[C] VERY SHORT ANSWER QUESTIONS:
(1 MARK EACH)
1. What is endemism in terms of species distribution?
Ans. Endemism means that species confined to a particular region and not found anywhere else.
2. Give two examples of invasive weed species that threatens our native species.
Ans. Carrot grass (Parthenium) & water hyacinth (Eichorna).
3. Since the origin of life on earth how many episodes of mass extinction occurred?
Ans. Five episodes of mass extinction occurred.
4. Write the equation of Species Area relationships in a logarithmic scale.
Ans. Log Slog C + Z log A.
5. Name the important, components of Biodiversity.
Ans. Genetic diversity, species diversity and ecological diversity.
6. Write the name of the Biodiversity Hotspots that cover exceptionally high biodiversity regions of North-east India.
Ans. Indo-Myanmar or Indo Burma and Himalayas
7. What do you understand by “Sacred Groves”?
Ans. Sacred groves are patches of forests where local tribals do not allow use of axe and sickle because of the religious sanctity attached to them.
8. Amongst the animals which is the most species rich taxonomic group?
Ans. Insects.
9. What is ex situ conservation?
Ans. Ex situ conservation is the approach in which threatened animals and plants are taken out from their natural habitat and placed in special setting where they can be protected and given special care.
10. What is it called where animals and plants are conserved in their own habitat?
Ans. In situ conservation.
11. Write anyone importance of bio-diversity.
Ans. Human beings derive countless direct economic benefits from nature such as food, firewood, fibre, industrial products and products of medicinal importance.
12. What is species diversity?
Ans. Species diversity is the variety of species and their relative abundance present within a region.
13. Give the biological name of the African catfish, which is introduced in the Indian water bodies for aquaculture purposes and is threatening the existence of the indigenous cat fishes.
Ans. Clarias gariepinus.
[D] SHORT ANSWER QUESTIONS (2 MARKS EACH)
1. Write briefly on the three levels of biological diversity.
Ans. The three levels of biological diversity are
(i) Genetic diversity: A single species might show high diversity at the genetic level over its distributional range. The genetic variation shown by the medicinal plant Rouwolfia vomitoria growing in different Himalayan ranges might be in terms of the potency and concentration of the active chemical (reserpine) that the plant produces.
(ii) Species diversity: The diversity at the species level. Fore eg the Western Ghats have a greater amphibian species diversity than Eastern Ghats.
(iii) Ecological diversity: At the ecosystem level, India with its deserts, rain forest, mangroves, estuaries and alpine meadows have a greater ecosystem diversity than a Scandinavian country like Norway.
2. State the importance of species diversity to the ecosystem.
Ans. i) Communities with more species, generally tend to be more stable than those with less species.
ii) Ecosystem with more species showed less year to year variation and total biomass.
iii) Increased biodiversity provides resilience to the ecosystem agains occasional, natural or made man difference and invasion by alien species.
3. Why it is dangerous to introduce alien species in an area?
Ans. When alien species are introduced in an area some of them turn invasive and cause decline or extinction of indigenous species. Though these plants are often introduced for their economic use but are considered to be a major cause for extinction of species.
4. How habitat fragmentation causes depletion of biodiversity?
Ans. Human settlements, building of roads, digging of canals and other development activities result in fragmentation of large sized habitats like forest. Fragmentation reduces the core area and increases the edge area. As a result mammals and birds requiring large territories and certain animals with migratory habits are badly affected leading to population declines. Most of them tend to disappear as their habitat area shrinks due to fragmentation.
5. Define coextinction.
Ans. When a species becomes extinct, the plant and animal species associated with it in an obligatory way also become extinct. When a host fish species becomes extinct, its unique, assemblage of parasites also becomes extinct.
6. Give the definition of protected areas.
Ans. They are biogeographical areas where biological diversity alongwith natural and associated cultural resources are maintained and protected against exploitation and poaching through legal and other effective measures. There are three types of protected areas national parks, wildlife sanctuaries and biosphere reserves.
7. What is national park? How many national parks are there in Assam?
Ans. National parks are specified areas created through legislation to conserve the natural and historical objects of national significance and conserve the wildlife present in that area.
There are 5 national parks in Assam Kaziranga, Manas national park, Dibru Saikhowqa, Nameri and Orang.
8. State the role of Zoos and botanical gardens in ex situ conservation.
Ans. Zoos and botanical gardens serve the purpose of protecting the threatened animals and plants under special care.
There are many animals that have become extinct in the wild but continue to be maintained in zoological parks. Botanical gardens protect live plant specimens. All modern botanical gardens have seed gene banks, tissue culture labs and other technologies for storing and growing germplasm.
9. Give the faunal elements of Pabitora wildlife sanctuary.
Ans. The faunal elements of Pabitora wildlife sanctuary include one horned rhinoceros, Asiatic buffalo, leopard, wild bear, Civet cat, Wild bear, Barking deer and many other animals. It is also home to more than 2000 migratory birds and various reptiles.
[E] SHORT ANSWER QUESTIONS (3 MARKS EACH)
1. “India is one of the 12 mega diversity countries of the world” explain the statement.
Ans. India has only 2.4% of the world’s land area, its share of the global species diversity is on impressive 8.1%. That is what > makes India one of the 12 mega diversity countries of the world. Newly 45,000 species of plants and wice as many of animals have been recorded from India Considering May’s global estimates that only 22% of the total species have been discovered by now, the number of organisms yet to be discovered in India can be more than 1,00,000 plants and more than 3,00,000 animals.
2. Write briefly on the diversity of tropical Amazonian rain forest of South America.
Ans. The tropical Amazonian rain forest of South America has the greatest biodiversity on earth. It is home to more than 40,000 species of plants, 3000 of fishes, 1,300 of birds, 427 of mammals, 427 of amphibians, 378 of reptiles and of more than 1,25,000 invertebrates. Scientist estimate that in these rain forest there might be at least two million insect species waiting to be discovered and named.
3. Explain the “Rivet Popper Hypothesis” in the context of extinction of species.
Ans. The effect of reduction in biodiversity has been explained by Paul Ehrlich through rivet popper hypotheisis. In an airplane (ecosystem) all parts are joined together using thousands of rivets (species). If every passenger travelling in it starts popping a rivet to take home (causing) a species to become extinct), it may not affect the flight safety (proper functioning of the ecosystem) initially, but as more and more rivets are removed, the plane becomes dangerously weak over a period of time. Furthermore, loss of rivets on the wings (key species that drive major ecosystem functions) obviously becomes a serious threat to flight safety.
4. What are the consequences of loss of biodiversity?
Ans. The consequences are
(i) decline in plant production
(ii) lowered resistance to environmental perturbations such as drought
(iii) increased variability in certain ecosystem processes such as plant productivity, water use and pest and disease cycles.
5. Give the ethical arguments for conserving biodiversity.
Ans. The ethical argument for conserving biodiversity relates to what we owe to millions of plants, animal and microbe species with whom we share this planet. Philosophically or spiritually we need to realise that every species has an intrinsic value, even if it may not be of current or any economic value to us. We have a moral duty to care for their well being and pass on our biological legacy in good order to future generations.
6. Give a brief account of International convention and Summit held for cause of conservation of biodiversity and sustainable development.
Ans. Biodiversity knows no political boundaries and its conservation is therefore a collective responsibility of all nations. The historic convention on Biological Diversity (The Earth Summit) held in Rio de Janeiro in 1992, called upon all nations to take approprioate measures for conservation of biodiversity and sustainable utilisation of its benefits.
In a follow up the World Summit on Sustainable Development held in 2002 in Johannesburg. Sourth Africa, 190 countries pledged their commitment to achieve by 2010, significant reduction in the current rate of biodiversity loss at global, regional and local levels.
7. Write a note on biosphere reserve with special reference to Assam.
Ans. They are large tracts of protected land with multiple use preserving the genetic divesity of representative ecosystem by protecting wildlife, traditional life styles of the tribals and varied plant and animal genetic resources. They have been set up under MAB programme of UNESCO starting in 1975. In India the first biosphere reserve to be established was Nilgiri biosphere reserve in 1986. In India 14 biosphere reserves had been established by then. They are also included under the category of national parks. Qut of these four have been included in the World network of Biosphere Reserves. In Assam there are two bioshere reserves. They are Manas and Dibru Saikhowa.
8. Make a list of six endangered animal species of Manas National Park.
Ans. Assam Roofed turtle, Hispid Hare, Golden Langur, Pigmy Hog, Bengal Florican, Capped Langur.
9. List the different elephant reserves of Assam.
Ans. The elephant reserves of Assam are-
(i) Sonitpur (Nameri)
(ii) Dehing-Patkai
(iii) Kaziranga- Karbi Anglong
(iv) Dhanseri- Lungding
(v) Chirang- Ripu
[F] LONG ANSWER QUESTIONS (5 MARKS EACH)
1. Why does the tropics represents great biological diversity? Explain.
Ans. Tropics represent great biological diversity because of the following reasons
(i) Speciation is generally a function of time, unlike temperate regions subjected to frequent glaciations in the past, tropical latitudes have remained relatively undisturbed for millions of years and thus had a long evolutionary time for species diversification.
(ii) Tropical environments, unlike temperate ones are less seasonal, relatively more constant and predictable. Such constant environments promote niche specialisation and lead to a greater species diversity.
(iii) There is more solar energy available in the tropics, which contributes to higher productivity this in turn might contribute indirectly to greater diversity.
2. Explain the Species-Area relationships with the help of graph.
Ans. German naturalist and geographer Alexander van Humboldt observed that within a region species richness increased with increasing explored area but up to a limit. The relationship between species richness and area for a wide variety of taxa (like vascular plants, birds, bats and freshwater fishes) appears as a rectangular hyperbola. On a logarithmic scale, the relationship is a straight line described by the following equation,
log S = Log C + Z log A
Where S = species richness
A = Area
Z = Slope of the line (regressin coeffecient)
C =y-ntercept.
The value of Z lies in the range of 0.1-0.2 regardless of taxonomic group or the region. However, the analysis in a very large area like the whole continent gives a Z value that ranges from 0.6 to 1.2.
3. Write note on the causes of biodiversity losses.
Ans. There are four major causes of biodiversity loss. They are (i) Habitat loss and fragmentation: Destruction of habitat is the primary cause of extinction of species. The tropical rainforest initially covered 14% of the land surface of earth, but now cover only 6% of land area. The Amazon rainforest is being cut and cleared for cultivation of soyabeans and for conversion into grasslands for raising beef cattle, When large sized habitats are broke, or fragmented due to human settlements, building of roads etc the population of animals requiring large territories and some animals with migratory habitats decline.
(ii) Over exploitation: When biological system is over exploited by man for the natural resources, it results in degradation and extinction of the resources. eg. Stellar’s sea cow, passenger pigeon etc.
(iii) Alien species invasion: Some alien species when introduced unintentionally or deliberately, become invasive and cause harmful impact resulting in extinction of the indigenous species. For eg. Nile Perch, a large predator fish when introduced in Lake Victoria caused the extinction of an ecologically unique, species of Cichlid fish in the lake.
(iv) Coextinctions: When a species becomes extinct the plant and animal species associated with it in an obligatory manner also became extinct. For eg. in plant pollinator mutualism, extinction of one results in the extinction of the other.
4. Explain why biodiversity should be conserved?
Ans. There are three main reasons for conserving biodiversity-
(i) Narrowly utilitarian reasons: Human beings derive direct economic benefits from nature like food. firewood, fibre, industrial products (resins, gums, dyes etc). More than 25% of the drugs are derived from plants and about 25,000 species of plants are used by native people as traditional medicines,
(ii) Broadly utilitarian rreasons: Biodiversity plays a major role in maintaining and sustaining supply of goods and services from various species as well as ecological systems. Amazon forest is estimated to contribute 20% of the total oxygen in the atmosphere on earth. Ecosystem provides pollinators like bees, bumble bees, birds and bats which pollinate plants to form fruits and seeds. Aesthetic pleasures like bird watching, spring flowers in full bloom, etc are some other benefits of the ecosystem.
(iii) Ethical reasons: There are thousands of plants, animals and microbes on this earth which are not, useless. Everyone has some intrinsic value even if it not of any economic value to us. It is therefore, our moral duty to ensure well being of all the living creatures for the utilisation of future generations.
5. What are the different ways by which biodiversity can be conserved?
Ans. There are two basic approaches for conservation of biodiversity-
(i) In situ conservation: This approach involved protection of species in their natural habitat. It is done in various ways –
(a) Biodiversity hot spots: These are regions of high levels of species richness and high degree of endemism. There are 34 hot spots in the world. In India, the three hot spots are Western Ghats and Srilanka, Indo Burma and Himalaya. These hotspots could reduce the ongoing mass extinctions by almost 30%.
(b) Protected areas: They are patches of forests where local tribals do not allow use of axe and sickle beoause of the religious sanctity attached to them. Large number of rare and threatened plants can be found in these regions.
(ii) Ex situ conservation: This approach involves placing threatened animals and plants in special care units such as zoological parks, botanical gardens and wildlife safaris for their protection. By using cryopreservation technique. Sperms. eggs tissues and embryos can be stored for long period in gener banks, seed banks etc. Plants are propagated invitro using tissue culture methods.
6. Write briefly on the pattern of biodiversity.
Ans. Biodiversity is not uniform throughout the would because
it is affected by two factors (i) Latitudinal Gradients: Species diversity decreases as we move away from the equator towards the poles. Tropics (23.5°N to 23.5°S) have more species than temperate or polar regions. For eg Columbia located near the equator has 1400 species of birds white New York (41.5°N) has 105 species and greenland (71°N) has only 56 species India with much of its land area in the tropical latitudes has more then 1200 species of birds. Tropical Amazonian rain forest in South America has the greatest biodiversity on earth.
(ii) Species area relationship: German naturalist and geographer Alexander von Humboldt observed that within a region species richness increased with increasing explored area but up to a limit. The relationship between species richness and area for a wide variety of taxa (like vascular plants, birds, bats and freshwater fishes) appears as a rectangular hyperbola. On a logarithmic scale, the relationship is a straight line. described by the following equation.
LogSlog C + ZlogA
The value of Z lies in the range of 0.1 0.2 regardless of taxanomic group or the region. However the analysis in a very large area like the whole continent gives a Z value that ranges from 0.6 to 1.2.
7. Write a note on Kaziranga National Park mentioning its important fauna.
Ans. Kaziranga National Park, the house of more than two third of the world’s one Southern bank of the river Brahmaputra. It covers an area of 430 sq.km. and is located in the districts of Golaghat and Nagaon and it about 75 m above mean sea level. To protect and rear only a dozen of rhinoceros at the beginning Kaziranga was declared as a reserve forest in 1908. Later in 1916 it was declared as game Sanctuary. It was again designated as Wildlife Sanctuary in 1950 and ultimately on 1st January, 1974 Kaziranga was accorded the status of a National Park.
Though the park is famous for Rhinos it has also rich variety of other mammalian, avian reptilian and piscian fauna. Amongst the mammals, the important species are Hoolock Gibbon, Capped Langur, Tiger, various species of Civets Bear, Indian Elephant,. Sambar, Wild Bear, Bison etc. 304 varieties of birds have been recorded such as Eagles, storks, Pelicans, Hornbill, Pheasants etc/ The reptilian Fauna includes Cobra, Python, Krate etc.
8. Write about Nameri National Park stating its important fauna.
Ans. Nameri national Park is located in the foothills of the eastern Himalayas in the Sonitpur district of Assam, India about 35 Km from Tezpur. The Park was declared a reserve forest on 17 October 1978. It was set up as a Nameri Sanctuary on 18th Sep. tember 1985 with on area of 137 Km² as a part of Naduar forest reserve. Another 75 Km² was added on 15th November 1998 when it was officially established as National Park.
It is considered as on elephant reserve. Also it is on ideal habitat for tiger, leopard Sambar Asiatic wild dog, Pygmy Hog, Wild Beoar, Sloth bear, Himalayan Black bear, Capped langur, Indian great squrrel. It is a bird’s paradise with over 300 sp. of birds such as white winged wood duck, Great Pied hornbill, Wreathed hornbill, Black stork, Babblers etc.
9. Describe the life cycle and rearing of eri silk moth.
Ans. The life cycle of eri silk moth is completed through eggs,. larva, Pupa in cocoon 8 adult moth-
(a) Eggs: A female moth after copulation lays about 300-500 eggs in a cluster which is covered by a hard chitionous white coloured shell. The laying may continue for 3 to 4 days but the eggs of first two days are only kept for rearing. The hatching of eggs takes place after about 10 days but it depends on the temperature of the environment.
(b) Larva: After hatching the larva tend to remain together. The newly hatched larva possesses a black coloured head and the body becomes yellow in colour but gradually changed to green yellow. The first moult occurs after three days. The larva matures in 17 to 45 days which depends on the environmental temperature and humidity. During this period, the larva moults four times. During the ouset of moulting, the larva becomes motionless and it does not feed. One moulting the integument of the head breaks on the sides and the larva comes out with a new integument. The larva pos- sesses a long tubular silk glands. In mature larva the silk gland occupies almost the whole body. This gland is responsible for the production of silk. The silk gland secretes the silky substance to form the cocoon.
In the cocoon the larva transforms into a chrysalid.
(d) Pupa: The spiming of cocoon beings with a semicircular movement of the head. In 3-4 days, the cocoon formation is com- pleted Inside the cocoon the larva transforms itself into a brown coloured chrysalid. It is an intermediate form between the larva and the moth. The essential organs of the moth are formed and those of larva are disintegrated in this stage.
(d) Moth: The moth emerges from the chrysalid after about 2 weeks. The moth comes out through the open end of the cocoon. After sometimes they fully stretch their wings. After stretching the wings the male finds out the female for mating which last about 24 hours. During mating the moths remain motionless. The male uhpairs in next evening. After unpairing the female lays the eggs normally during the night. A female moth lays about 300-500 eggs in cluster in 3-5 days. And the life cycle continued.
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Last Words on ASSEB/AHSEC Class 12 Biology Chapter:13 Biodiversity and Conservation
The Chapter 13 of ASSEB/AHSEC Class 12 Biology deals with Biodiversity and Conservation for a brief understanding. You can Download this HS 2nd Year Biology Notes in PDF 2025-26.